I don't think Sabo was seriously gambling with Luffy's life, as he's halfway unconscious and needing to be carried to safety.
That's the entire point though.
^Fujitora says that he is willing to risk his life for the resolution of Dressrosa event.
^he confirms Sabo is in same situation as him, that it is not their place to be heroes of the country.
^
Sabo accepts that they are making a gamble with this stunt.
If Sabo became main star in Doflamingo fight, it would destroy the entire purpose of Straw Hats saving the country.
We are blatantly told Sabo plays the same role as Fujitora, which is to "act" busy.